The anal canal acts as the end of the gastrointestinal tract. It is formed by the union of the hindgut (endoderm) and the proctodeum (ectoderm) with an intervening anal transitional zone. The borders of the anal transitional zone are the anorectal line proximally and the dentate line (a.k.a pectinate line) distally. Glands are found at the dentate line. The columns and sinuses of Morgagni and the internal hemorrhoids are located within the transitional zone. The anoderm is surround by two sphincters, internal and external. The internal sphincter, a continuation of the intestinal smooth muscle, is involuntary, while that of the external sphincter is voluntary. The blood supply and lymphatic drainage vary because of disparate embryologic origins.